What Would be the Aftermath of US Withdrawal?

What would happen if Coalition (at this point, that pretty much means US) forces left Iraq?

Well, some say that US forces are the only thing holding back even wider scale bloodshed – after all, in some areas where the US has lost complete control, attacks on civilians seem to be particularly bad.

Others say that US forces are what is keeping the fighting going. It doesn’t seem likely that US withdrawal would lead to the lion lying down with the lamb so to speak, but who knows, it might precipitate a more or less peaceful partition (a la India, Pakistan, and eventually, Bangladesh after the British left).

None of us knows for sure. But… the fact is, the administration and its supporters are the ones who are most insistent on the storyline in which the US is the one finger in the dam holding back the floodwaters. As others have pointed out before – the administration has been wrong on everything they’ve told us when it comes to Iraq so far (as well as everything about their other big ticket item, the tax cuts). So… why would they be right about this?

A few questions:
1. Can we reasonably assume that the administration is wrong because, well, they’ve always been wrong so far? Bear in mind that up until recently, they’ve been wrong about things being rosy. Are they also wrong when they say things would be awful?
2. What would happen if the US withdrew?
3. What should the US do when it comes to Iraq?